Boreholes for hydrocarbon (oil and gas) production, as well as for other purposes, are usually drilled with a drill string that includes a tubular member (also referred to as a drilling tubular) having a drilling assembly which includes a drill bit attached to the bottom end thereof. The drill bit is rotated to shear or disintegrate material of the rock formation to drill the wellbore.
Torsional vibration in the drill string and in downhole drilling tools forming part of the drill string is an undesired phenomenon that often occurs during drilling. It can cause incidents which include but are not limited to twist-offs, back-offs, and bottom hole assembly (BHA) component failures. Torsional vibrations can also affect readings taken during measuring while drilling (MWD) operations.
Torsional vibration is typically caused by variations in the rotational speed (RPM) of the rotating assembly comprising the drill string, often experienced as stick-slip phenomena. Stick-slip behavior can be induced by a number of causes, including lateral vibrations and changes in rock formation type.
Lateral vibrations can cause a drill bit box and/or drill string stabilizers to make contact with a borehole wall to a varying extent. Friction between the drill string and the formation resulting from contact with the wellbore by these components often causes fluctuations in speed, exciting torsional vibration in the drill string. Similarly, fluctuations in the hardness of the formation along the borehole can vary the extent to which full gauge stabilizers in the drill string can rotate freely, thus intermittently varying the drill string's rotational speed. Such fluctuations in rotational speed of the drill string, as well as torsional shock impulses propagated along the drill string due to torsional vibration and/or associated stick-slip phenomena is detrimental to the structural integrity of drill string components and can cause or hasten failure of drill string components.